The problem of waste tires accumulating has grown dramatically and now presents a significant environmental concern. Waste tires occupy a great deal of space in garbage dumps and landfills and constitute a contributing factor to a huge increase in generated waste that is causing the swelling of landfills. At present, over 230 million waste tires accumulate annually, with approximately 3 billion accumulated to date.
The proliferation of waste tires generated annually has given rise to a search for an efficient and clean method to reduce the volume of waste tires. One method investigated extensively is heating the tires sufficiently to break them down into solid and fluid components, a process known as pyrolysis. The benefits realized are two-fold. First, many of the solid and fluid components can be recovered after pyrolysis and recycled to produce useful products. Secondly, the volume of waste products resulting after pyrolysis that are not recyclable is much less than that of the original waste tires. This helps slow the swelling of landfills.
In many instances, however, pyrolysis of waste tires is not feasible because of excessive energy costs incumbent in raising the tires to a high temperature. These energy costs are generally greater than any benefit accruing from reducing the flow of waste products to a landfill or revenue produced from the pyrolysis products. In addition, there are high costs associated with the disposal of toxins produced during pyrolysis, further frustrating utilization of this method for reducing the volume of waste tires.
An attempted solution to the problem of high excessive energy costs is to pulverize the tires into small pieces to (1) fit more efficiently into a heating chamber and (2) increase the surface area exposed to the heat. This procedure is particularly utilized with standard convection heating pyrolysis apparatus wherein the heat is transferred to the tires from the outside surface inward.
Another attempt to reduce excessive energy costs associated with pyrolysis is to include a preheat section prior to the pyrolysis section to ease the heating requirements of the pyrolysis section.
More recent innovations in the pyrolysis of waste tires have resulted in faster and more efficient heating and break down into solid and fluid components. Specifically, microwave energy is applied to heat the waste material as opposed to convection heating. Microwave energy is applied uniformly throughout the tire materials to heat them more uniformly and rapidly than with convection heating. Microwave heating thus eliminates the need for the tires to be pulverized. U.S. Pat. Nos. 5,084,140, 5,084,141 and 4,839,151 disclose pyrolysis applications utilizing microwave energy.
Another recent innovation in waste material pyrolysis is the recycling of hot gases generated in the pyrolysis heating chamber into a preheat section. Subsequent waste material passes through the preheat section prior to the pyrolysis section and is preheated therein so that less heating, and less energy is required in the pyrolysis section. The heating efficiency utilizing the recycled hot gas is improved because less energy is required overall. The '141 patent demonstrates a pyrolysis assembly with hot gas produced during pyrolysis recycled into a preheat section. In addition, U.S. Pat. No. 3,926,582 discloses a pyrolyzing assembly wherein the hot gas produced is utilized to drive a generator to provide electric energy.
Another disadvantage of prior art pyrolysis apparatus is that they are permanently constructed on a particular site, so waste material must be transported to that site for processing. In instances wherein waste tires are found in numerous landfills extending over wide areas the cost of collecting and transporting the waste tires to the site of the pyrolysis apparatus is prohibitive.